Treatment of hydrocarbons

ABSTRACT

Charge aromatic streams, such as C6-C11 aromatic streams, may be treated to separate a C7-C8 stream, a benzene stream, and a heavier stream. At least a portion of the heavier stream is treated to lower its content of fused polycyclic hydrocarbons; and the denuded heavier stream is transalkylated with the benzene stream. The remaining portion of the heavier stream is dealkylated to give increased yield of C7-C8 aromatics.

United 511a if: BEST AVA'LABLE CQPY 1 1 3,927,136

x 5' O 1 .1 Sugg1tt et al. X ,2 Dec. 16, 1975 21-" J m 1 [54] TREATIVIENT OFDHYDROCARBONS 2,480.939 9/l949 Lee et al 260/672 7 [75] inventors: Robert M. su m, wappin 21522122; 31322 fiillfffliifliijiiiijiijiiiijj'i 5281235 Falls; John D. Odie, Poughkeepsie, both of Primary Examiner-Delbert E. Gantz {73] Assignee: Texaco Inc., New York, NY Assistant Examiner-C. E. Spresser Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries' 7 1 y 1 [-2] F1led. July 5, 1974 Car] G Seutter [21] Appl. No.: 485,857

{57] ABSTRACT 260/672 R; 260/672 gggz g Charge aromatic streams, such as C ,-C aromatic streams, may be treated to separate a C -C stream, a [58] F'eid of Search 260/672 672 672 T benzene stream, and a heavier stream At least a portion of the heavier stream is treated to lower its con- [56] References cued tent of fused polycyclic hydrocarbons; and the de- U D STATES PATENTS nuded heavier stream is transalkylated with the ben- 2,383.072 8/1945 Oblad 260/672 zene stream. The remaining portion of the heavier 2,389.713 11/1945 Atwell .1 260/672 stream is dealkylated to give increased yield of C -C 2.399.780 5/1946 Arnold 260/672 aromatics, 2,399,781 5/l946 Arnold 260/672 I 2,416,184 2/1947 Lee et a1 260/672 13 Claims, 1 Drawing Figure M,swi 7 y M Desi Vegans m shc @j 6:

BEST AVAILABLE COPY TREATMENT OF HYDROCARBONS FIELD OF THE INVENTION This invention relates to the preparation of hydrocarbons. More specifically it relates to a process for recovering toluene or C aromatics from aromatic feeds containing benzene. toluene, and C C C and C aromatics.

BACKGROUND OF THE INVENTION As is well known to those skilled in the art, during processing of petroleum-derived fractions there may be obtained various aromatic fractions containing C C C C and higher cuts. One typical aromatic fraction which may be so obtained contains predominantly aromatic hydrocarbons having 6-11 carbon atoms. Still another aromatic fraction which may be obtained, referred to as crude xylenes, actually contains hydrocarbons having 79 carbon atoms.

Refinery operations in which high grade gasolines are to be produced may recover aromatic fractions containing predominantly 6-8 carbon atoms referred to as a BTX fraction containing substantial quantities of benzene, toluene, xylenes, and ethylbenzene.

In processing each of these fractions, it is commonly desired to rwover each of the components to permit most eflicient utilization of the separated components. In the case of the crude xylenes, it may be desirable to recover substantially pure xylenes free of C-, and C cuts.

in the case of a BTX charge, it may be desirable to recover the toluene and C aromatics to permit eg use in g'asolines and to thereby upgrade the latter in paru'cular to increase the back end volatility which improves the drivability of new cars during engine warmupQMore particularly the possibility of more severe restrictions on the end point of motor naphtha raises aproblem which may be solved by the presence of increasing proportions of toluene in motor fuels with decreased proportions of benzene and xylenes.

Treatment of these typical stream to upgrade them may commonly include transalkylation wherein typically a Q, stream and a C and heavier stream may react to produce increased yield of a desired C -C stream. Transalkylation may be carried out in the presence of a catalyst which may include a Group VIII metal on a support Typical of such catalyst may be that including 7% cobalt sulfide on 40:1 SiO,:Al,O acid leached mordenite and of an alumina matrix. Another typical catalyst may include 80% of a silica-alumina matrix and of 2% platinum on 40:1 SiO :Al O acid leached rnordenite.

As transalkylation is carried out under predetermined conditions of temperature, pressure, flow rate etc., it is found that the yield of eg toluene decreases with time and especially so when the catalyst is in contact with a stream containing C and heavier cornponenm. Typically for example, when using the abovementioned cobalt catalyst to make toluene from benzene and xylene at 650F, 800 psig and total Ll-ISV of 6 (equimolar amounts of benzene and xylene), the yield may be 40%. After 200 hours, the yield may decrease to 35%. After 500 hours, the yield may be When this latter yield is reached, it may be necessary to reactivate or regenerate the catalyst.

Although the deactivation of the catalyst may be a result of several factors, it is found that continuing operation is accompanied by a build-up of carbon on the catalyst. Typically it is found that as the carbon content increases from its initial value of below about 0.2% to a value of about 2l0%, say 5%. the yield may decrease from its initial value of typically about 40% to an undesirably low value of 20-357c, say 30%. This undesirable decrease in catalytic activity imposes an undesirable economic burden on the Operation.

It is an object of this invention to provide a process for transalkylation. lt is another object of this invention to provide a transalkylation process characterized by increased catalyst life. Other objects of this invention will be apparent to those skilled in the art.

STATEMENT OF THE INVENTION In accordance with certain of its aspects. the method of this invention for treating a charge aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component may comprise a. fractionating said charge aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component;

b. separating fused polycyclic hydrocarbon component from at least a portion of said fractionated stream containing said heavier component and said polycyclic hydrocarbon component thereby forming (i) an enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component and (ii) a denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component;

c. combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) less than all of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalkylation charge stream containing (i) lighter component, (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon thecontent of heavier component in said transalkylation charge stream;

d. transalkylating, at transalkylating conditions in the presence of transalkylating catalyst, said transalkyla tion charge. stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, and (iii) a lighter component containing a smaller number of carbon atoms than does said middle component; and

e. withdrawing said transalkylate product stream.

DESCRIPTION OF THE INVENTION The process of this invention may preferably be used to treat a charge containing a significant proportion of aromatic content; and such charge stocks may be prepared typically by extracting aromatic components from the effluent from a reforming operation or from the pyrolysis or hydrogenation of coal or its extracts.

The feed to a reforming operation, typically a catalytic reforming operation, may be naphtha, preferably a straight run naphtha such as a full boiling range naphtha derived from atmospheric pressure distillation of crude oil in a crude topping unit.

Typically a feed naphtha stream may be character- In a preferred embodiment the feed naphtha may be passed to a reforming operation, preferably a catalytic nforrning operation, wherein reforming is carried out at 850-975F, say 920F at -800 psig, say 300 psig with a WHSV of -10, say 2.8 and a hydrogen to hydrocarbon mole ratio of 2-10, say 7. The preferred catalyst may be e.g. a noble metal on alumina, typically 0.4% Pt-O.2% rhenium.

Reformate may be characterized by the following criteria:

p y Broad Range Typical API Gravity 35-60 45 [HP "F 80-150 1 10 E? "F 350-450 410 RON Clear 80-105 100 Aromatics vol. 30-75 68 Naphthenes vol. 5 0-20 4 hratfins vol. 5-60 28 0-5 0 *lhe refonnate is passed to a separation operation,

, preferably an extractive distillation operation, typically a Udex unit, wherein aromatics may be separated from non-aromatics. Reforrnate may for example be containted with aqueous glycols to permit attainment of aromatic extract typically characterized by the following criteria:

W Broad Range Typical API Gravity 30-60 33 [DP F 176-350 176 E? F 250-500 410 Aromatic: vol. l1 80-l00 98 Naphthenes vol. 1: 0-5 I Parzffins vol. X: O-lO l Oiefins vol. I: 0-5

Although such a charge aromatic stream may be typical of those which may be treated by the preferred process of this invention, other streams containing hydrocarbons having e.g. 6-12 carbon atoms may be employed-such as coal pyrolysis liquids, or the extract BEST AVAILABLE COPY of aromatics obtained from the destructive hydrogenation of coal, tar sands, shale oil, etc.

An illustrative C -C stream might contain the following:

The charge stream contains a middle component as well as a heavier and a lighter component, the latter two having respectively a larger number and a smaller number of carbon atoms than does said middle component. Thus the charge stream may contain a benzene light component, a toluene middle component, and a trimethylbenzene heavy component. In one embodimerit, the heavier and lighter components may contain respectively more and less alkyl groups than does the middle component. Such a system may include e.g. benzene, toluene, and methylethylbenzene as lighter, middle, and heavier components. In the preferred embodiment however, the several components may contain the same alkyl group (e.g. methyl); and the lighter component may contain a smaller number of alkyl groups (eg none as in the case of benzene) and the heavier component may contain a larger number of alkyl groups (eg 2-3 as in the case of xylenes plus trimethylbenzenes) than does the middle component typically toluene.

Preferably the charge contains less than about 20% non-aromatics and more preferably less than about 2% non-aromatics. It is also preferably free of oxygen and nin'ogen.

In addin'on to the major components of the various charge streams noted supra, it is found that they commonly contain about O.1-5%, say about 1% of fused polycyclic, typically dicyclic, hydrocarbons commonly containing at least one aromatic ring. These fused dicyclic hydrocarbons may have boiling points above 349F, typically 352-500-l-F.

Illustrative of these fused polycyclic hydrocarbons may noted the following:

Compound Boiling Point 'F Naphthalene 424 Tetraliri 405 Methyl-naphthalenes 466-472 Ethyl-naphthalenes 496-500 Dimethyl-naphthalenes 514 lndan 352 lndene 360 yi indans 369-374 Methyl indenes 368-388 aromatic hydrocarbon component-typically xylene or In practice of the process of this invention. the charge aromatic hydrocarbon stream contains (i) a middle component, typically toluene, (ii) a lighter monocyclic aromatic hydrocarbon component, typically benzene containing a smaller number of carbon atoms than does said middle component, (iii) a heavier inonocyclic alkylaromatic hydrocarbon component. typically xylenes containing more carbon atoms than does said middle component. and (iv) 0.l-5% (by weight of the heavier monocyclic alkylaromatic component) of the fused polycyclic hydrocarbons containing at least as many carbon atoms as does said heavier component.

In practice of the process of this invention, in accordance with certain of its aspects, the charge aromatic hydrocarbon stream, commonly containing (i) l-lO moles, say 2 moles of a lighter component typically benzene, (ii) 0-20 moles, say 8 moles of a middle component, typically toluene, (iii) 3-20 moles, say 12 moles of a heavier component, typically xylenes, and (iv)'0. 1-5 weight percent, say 2 weight percent of fused polycyclic hydrocarbon component, (based on heavier component), is passed to a fractionation operation.

In the fractionating operation, the charge aromatic hydrocarbon is fractionated to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component.

In a preferred embodiment, this is carried out in a fractionating operation wherein for example in a first charge rectifying tower there may be recovered as bottoms, a stream containing the heavier component and the fused polycyclic hydrocarbon component. The overhead, containing the middle component and the lighter component, may be further distilled to produce bottoms containing the middle component and overhead containing the lighter component. In an alternative embodiment, the first tower overhead may be lighter component the distillation of the bottoms therefrom in a second tower producing heavier component (including fused polycyclic hydrocarbon component) a bottoms and middle component as overhead. In a further alternative embodiment, this separation may be carried out in one tower with sidestream stripping to obtain the desired three products which in the preferred embodiment may be essentially (i) benzene, (ii) toluene, and (iii) xylene plus fused polycyclic hydrocarbon.

In typical operation, there may be obtained 3-10 moles, say 8 moles of a first stream containing the lighter component and having the following characteristics:

Component Broad Typical Benzene wt. l: 60-100 90 Toluene wt. '17 O-BO 10 Xylene wt. k 0-10 0 Other 0-1 0 Broad Component Typical Benzene wt.

BEST 6WA|LABLE coPY -continued Component Broad Typical Toluene wt. 7: 10-100 99 Xylene wt. 7: (3-20 5 Other 0-] (i There is also obtained 10-50 moles, say 3. moles of a third stream containing the heavier component and In practice of the process of this invention, it will be found that the total quantity of heavier component (e.g. xylene) in the third stream may be substantially more than is equivalent to (i.e. it may contain more than 100 mole of) the total molar quantity of the lighter component to be admitted to the transallzylation operation.

It is however a particular feature of the process of this invention that, prior to transalkylation of the several streams as described in detail infra, the content of fused polycyclic hydrocarbon components, present in the sn'eam containing the heavier component, be lowered from its initial value of 0. 1-5%, say 1%, to a lower level of 0-O.3%, preferably 0-0.2%, say less than about 0.1% (based upon the weight of heavier component).

At least a portion of the fractionated stream containing the heavier component and the polycyclic hydrocarbon component may be separated into (i) an enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component and (ii) a denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component.

The portion subjected to separation may be 5-l0O% of the total of the fractionated stream containing the heavier component and the fused polycyclic hydrocarbon component depending on the need for denuded heavy component.

In the preferred embodiment, the stream may be separated by distillation. Preferably distillation is effected to produce an overhead having an end-point of about 345F or less.

In the preferred operation, this charge stream may be heated and passed to a distillation column. Bottoms may contain a portion of the fused polycyclic hydrocarbons in the charge. In a typical operation, this bottoms is an enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing the heavier component and the fused polycyclic component.

It may typically (in the case of an original BTX charge) contain C such as xylenes, C, aromatics, fused polycyclic hydrocarbons, etc.

Overhead, withdrawn from the tower, containing principally xylene. is condensed against water; and a portion may be returned as pumped reflux to the tower. This overhead stream may be a denuded stream of the heavier component containing a lesser amount of said fu ed polycyclic hydrocarbon component than said fractionated streamcontaining said heavier component and the fused polycyclic component.

It will be apparent to those skilled in the art that the xylene separation operation be conducted. in the preferred embodiment so that the amount of fused polycyclic hydrocarbons recovered as bottoms from this operation be such that when the overhead (typically xylene) is combined with the light stream from the fractionating operation, the content of fused polycyclic hydrocarbons (based on the content of heavier eg xylene component) may be maintained at reduced levels preferably less than about 0.1% by weight in the transalkylation charge stream.

lt will thus be apparent to those skilled in the art that the separation operation may be conducted only to a degree of efficiency to remove a minimum amount of fused polycylids from the chargethereto containing the heavier component. The overhead, denuded stream, may contain fused polycyclic hydrocarbons although in lesser amount than does the bottoms enriched with respect to these latter. Clearly also, the bottoms may contain substantial portions of heavier component. This separation may be carried out in a distillation tower.

in the preferred embodiment, at least a portion (-10070, more preferably all) of the denuded stream may be combined with less than all (typically O95%) of the fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component.

There is then combined with the so-forrned combined heavy stream, the equivalent quantity of the stream containing said lighter component recovered from said fractionation thereby forming a transalkylation charge stream. In the preferred embodiment, all the stream containing the lighter component recovered from fractionation may be passed to the transalkylation :icharge stream together with an equivalent amount of heavier component (the latter including preferably all the denuded stream from separation overhead plus enough of the unseparated stream from fractionation containing fused polycyclic hydrocarbons to provide the noted equivalent amount of heavier component) the amount of fused polycyclic hydrocarbons in the charge to transalkylation being decreased to desired value which is less than that contained in the fractionated stream of heavier component. It will be apparent to those skilled in the art that this invention permits ready attainment of the target desiderata with maximum of flexibility. Thus the proportion of heavier stream (containing undesired fused polycyclics) which is to separation and the degree of separation be varied depending upon the particular charge 8 content of heavier component) is less than the content there of in the fractionated bottoms. It may be less than about 0.1%, typically 0.0l-0.05%, say 0.05% by weight.

Thus in the preferred operation the combined stream, which serves as the charge monocyclic alkylaromatic hydrocarbon stream to the transall-tylation operation may, in the preferred embodiment, be a benzenexylene stream substantially free of fused polycyclic hydrocarbon components, and may typically contain benzene, toluene, xylenes, and fused polycyclic aromatics.

In practice of the preferred aspects of the process of this invention, the charge to transalkylation will contain less than about 0.1 wt. of polycyclic fused hydrocarbons based on the weight of the heavier monocyclic alkylaromatic hydrocarbon, typically xylenes.

Transalkylation may be carried out at temperature and pressure which depend on the particular catalyst system used. It may be effected at 500-ll00F say 625F and -2000 psig, say 800 psig at LHSV of l-l5, say 4 with hydrogen to hydrocarbon mole ratio of 2-15, say 4.

Transalkylation catalyst may include a Group VIII metal on an acid support. Although the metal may be a noble metal such as ruthenium Ru, rhodium Rh, palladium Pd, osimum Os, iridium Ir, or platinum Pt. it may more preferably be nickel Ni, iron Fe, or cobalt Co. Typical acid supports may include hydrogen mordenrte.

The preferred catalyst may include 15% of alumina matrix in which 7% cobalt sulfide is dispersed on 78% of a 40:1 SiO :Al O acid leached mordenite.

Sufficient sulfide is present in the feed to retain the Group VIII metal in the sulfide form. For example 0.5% sulfur (as H 5), present in the hydrogen stream maintains the cobalt in the sulfide form over the normal range of operating conditions.

Transallcylate may typically contain benzene, toluene, xylenes, and polycyclics.

In the preferred embodiment, the transalkylate product stream may be passed to the fractionation operatron.

It is a feature of this invention that transalkylation may be carried out for extended times at high levels without regeneration. Typically for example such operations may permit catalysts to have useful half-lines of more than 100 hours and preferably more than 200 hours (the useful half-life is defined as the time for the conversion to decrease to one half of the initial linedout value).

Maintenance of the content of polycyclic fused hydrocarbons below 0.1% by weight in the feed permits attainment of unexpected gdvantages. For example with a typical transalkylation catalyst over the C08 on mordenite at fixed reactor temperature of say 600F, the useful half-life as a function of content of polycyclic fused hydrocarbons may be as follows:

Content of Naphthalene Half-Life (hrs) 1% 10 hours 03% about 24 0.1% about 100 0.005% over 300 In typical commercial operation, it may be found that the novel technique of this invention permits increase 9 in the useful period (during which a catalyst may be used prior to regeneration).

lt is also found that continuing operation may be carried out at lower temperature. Prior commercial practice may include the use of higher temperature as the catalyst is rendered less operative by the build-up of carbon. resinous material etc.

The third portion of the fractionated stream containing the heavier component and the fused polycyclic hydrocarbon component (the first portion thereof having been passed to separation and the second portion thereof being combined to form the transalkylation charge) in amount of -95%, typically EEO-70%, of the said fractionated stream may be passed to a dealkylation operation.

It is a feature of the process of this invention according to certain of its aspects that there may also be added to the third portion of the fractionated heavier component containing the fused polycyclic hydrocarbons, at least a portion of the enriched stream of heavier component containing fused polycyclic hydrocarbon component, to form the charge to dealkylation.

It is a feature of the process of this invention that presence of the fused polycyclic hydrocarbons is unexpectedly found to be undesirable during transalkylation but is much less undesirable during dealkylation. Thus each reaction may be carried out separately to maximum advantage with attainment of maximum life of catalyst.

The total charge to dealkylation typically includes the several streams consisting essentially of the heavier components such as C C etc. aromatic components.

Typically deallcylation is effected as by thermal or catalytic hydrodealkylation; thermal or catalytic steam dealkylation, etc. In one embodiment for example hydrodealkylation is effected at ll0O-l300F, say 1250F and 300-500 psig, say 400 psig for -10 seconds, say 5 seconds with a hydrogen to hydrocarbon charge mole ratio of 2-10, say 5.

During dealkylation, the charge stream containing heavier components and having the typical composition supra may be dealkylated to form a dealkylated stream containing increased amounts of lower aromatic hydrocarbons such as benzene, toluene, etc. and lesser amounts of heavier aromatic components such as C C etc.

1n the preferred embodiment, the dealkylated stream having the dealkylation operation may be recycled to and combined with the charge aromatic hydrocarbon admitted to the first fractionation operation.

The proportion of the total of the heavier fraction which is. passed to dealkylation and the proportion which is passed to transalkylation may depend upon the operating parameters of the system and particularly upon the relative composition of the initial charge and the operation of the dealkylation and transalkylation steps and the products desired. In the preferred embodiment, there ma more heavy components within the than the equivalent amount necesti'ahsallcylate the light component to produce me desired iniddle component; and the excess of heavy component over that equivalent is charged to the dealkylation reaction.

Although it will be apparent to those skilled in the art that lighter or heavier component may be provided from outside sources to permit proper balance in the transalkylatioii operation, is a feature of the process of this invention in its preferred embodiment that deal- BEST AVAILABLE COPY kylation may preferably be employed to convert at least a portion of the heavier component (normally present in excess) to dealkylated components and to thus maintain a balance in the system.

DESCRIPTION OF A PREFERRED EMBODIMENT Practice of the novel process of this invention may be apparent from the following description of a preferred embodiment wherein, as elsewhere in this specification, all parts are parts by weight unless otherwise specifically noted. The accompanying drawing represents schematically a flow sheet of one technique whereby the process of this invention may be carried out. It will be apparent to those skilled in the art that the drawing may show major pieces of equipment, and that various pumps, valves, heat exchangers, collection drums, etc. may not be shown.

In the drawing the feed admitted through line 10 in amount of parts may be a naphtha stream charac- Catalytic reforming is carried out in operation 11 at average temperature of 920F and 300 psig with a WHSV of 2.8 and a hydrogen to hydrocarbon mole ratio of 7. The catalyst is 0.375% platinum 0.2% rhenium on alumina.

Reformate in line 12 is characterized as follows:

Property Value API Gravity 45 lBP "F l 10 EBP "F 4l0 RON Clear IOO Aromatics vol. 68 Naphthenes vol. 4 Paraffins vol. 36 28 Olefins vol. 0

The reformate is passed to Udex separation operation 13 wherein it is contacted with aqueous glycol to permit attainment in line 14 of an aroman'c extract characterized by the following criteria:

property Value APl Gravity 33 lBP. "F 178 Aromatics vol. 99

liaphthenes 1 More specifically, the stream in line 14 contains:

Component I .Parts by WeiglL Benzene 2.82

Toluene 15.98 Ethylbenieh'e 6.02 Xylenes 32.78 Propylbenzen'es 2.64 Ethyltoluenes l 1.30

BEST AVAILABLE copy TABLE-continued Component Parts by Weight It is to be noted that the C, fraction is relatively rich in ethylaromatics and consequently it is less preferable than the C stock for transalkylation against benzene to make toluene and xylenes. It is more suitable to use this Component Typical Light Gases 7.1 1 Benzene 18.10 Toluene plus 91.69 C. aromatics C, aromatics boiling up to 345F 36.60 Alkyl-C, aromatics boiling over 345? 2.26 lndan-indene 0.32 C alkyl benzenes l2.7l methyl indan-indenes 0.43 C and C 3.13 Naphthalenes 0.30 Non-aromatics 0.33 172.98

I 7.11 parts of light gases are flashed off (in a tower v i which is not shown); and the remainder of this stream is passed to rectifying tower 17. Net bottoms are withdrawn through line 18 in amount of 56.08 parts having the following composition:

Overhead is recovered from rectifying operation 17 through line 19. 109.79 parts of net distillate, recovered in line 19, have the following composition:

TABLE Component Parts by Weight Benzene 1 8. 1 0 Toluene 37 .34

C, aromatics 54.35

The purified BTX stream in line 19 is passed to benzene separation operation 20. 91.69 parts of net bottoms withdrawn through line 21, have the following composition:

TABLE Component Pans by Weight Toluene I 37.34 C. aromatics 54.35

It will be observed that there is no fused polycyclic aromatic in the stream in line 21.

Overhead from benzene separation operation 20 is withdrawn through line 22. 18.10 pans of condensate are passed through line 22; optionally benzene may be added or withdrawn through line 23. 1810 parts of net condensate pass through line 22 and thence through line 24.

In this embodiment, all of the stream in line 18 is passed through line 25 to separation operation 26. In the tower 26, separation occurs to give 34.00 parts of overhead containing C alkylbenzenes boiling below 345F and containing less than 0.02 parts (0.06%) of fused dicyclic aromatics such as indan-indenes.

This overhead is recovered in line 27 and 27.40 parts are passed through line 27. 6.60 parts may be passed through line 28.

The stream of heavier component plus fused polycyclic components in lines 43 and 43 may contain 22.08 parts having the following composition:

TABLE Component Pam lndan-indenes 0.30 methyl indan-indenes 0.43 C, alkyl benzenes 5.11 C alkyl benzenes l2.7l C -C alkyl benzenes 3.13 naphthalenes 0.30 nonaromatics 0.10

} TABLE Component Pam Benzene 18.10 Toluene 0 nonaromatics t 0.23 C. including xylenes O C, alkylbenzenes 27.155 Fused polycyclic hydrocarbons 0.015

total 45.50

It is a feature of the process of this invention that the stream in line 32 is particularly characterized by (a) the presence therein of heavier component e.g. C alkylbenzenes in amount substantially equivalent to the ligher component (benzene) and (b) the presence therein of only 0.06% of fused polycyclic hydrocarbon components (based on the C components).

In transalkylation operation 33, 18.10 parts of benzene from line 24 and 27.40 parts of C alkylbenzenes from line 31 (representing a 1:1 mole ratio of C alkylbenzenes to benzene) are transalkylated at f:650F, say 625F and 1000 psig, 3 LHSV and 4:1 hydrogen to hydrocarbon mole ratio. Catalyst contains as active component a 40:1 SiO :Al O acid leached mordenite bearing 7% cobalt sulfide in a alumina matrix. Effluent in line 34 contains 45.50 parts of product containing near equilibrium conversion of toluene and C aromatics.

Product recovered in line 34, in amount of 45.50 parts, typically has the following composition:

PARTS COMPONENT Light gases 0.58 benzene 8.38 toluene 13A] C, aromatics 12.45 C, aromatics 7.29 C aromatics 2.27 C aromatics 1.04 C, aromatics 0.08

The above-tabulated composition of product transalkylate (containing about 57% C and C is attained at the beginning of the active catalyst life i.e. as initially lined-out.

It '5 possible to measure the efifectivity of a catalyst by its ha1f1ife i.e. the time in hours at which the activity measured at standard conditions reaches a level of one-half the original lined-out level. The noted catalyst, when operating under the conditions of this preferred embodiment (including a content of less than 0.1 fused polycyclic hydrocarbons in the charge) may have an extended half-life.

Use of the same catalyst under comparable conditions but with a charge to transalkylation containing all 7 the fused polycyclic hydrocarbons originally present in the stream in line 14 typically gives lower lined out yields; more significantly however the half-life of the catalyst typically drops. It is a feature of the process of this invention that it permits attainment of improvement in catalyst half-life.

Transalkylate product in line 34 is passed through lines 35 and 15 to fractionating operation 17.

In common practice of the process of this invention,

BEST AVAILABLE COPY the stream in line 18 will contain more heavy alkylbenzene than is needed to transalkylate the benzene in line 22; and this excess of heavy alkyl benzene is passed through lines 29, 37, 38, 40, and 41 to dealkylating operating 42. Also excess C alkylbenzenes in line 27, beyond that needed in line 27 for Il'Lai-Stilli)l3ll0fl. may be drawn oii through lines 28 and 44 and 41 K c alkylation operation 42. In this example 6.60 parts of C alkylbenzenes in line 28 are combined with the 22.08 parts from line 43 (via 43' and 38 and 40) and are passed to dealkylation operation 42. The total feed in line 41 contains 28.68 parts having the following composition:

TABLE Components P C, alkylbenzenes 1 1.66 Indanindenes 0.30 methyl indan-indenes 0.43 C, alkylbenzenes 12.71 C,,C, alkylbenzenes 3.13 Naphthalenes 0.30 non-aromatics 0.15

The charge to dealkylation includes 1.03 parts of fused polycyclic aromatic hydrocarbon out of a total of 28.68 parts.

In this preferred typical embodiment, 28.68 parts of dealkylation charge in line 41 are passed to dealkylating operation 42 wherein dealkylation is effected at 1lO0-l300F say 1250F and 300-500 psig, say 400 psig for 05-10 seconds, say 5 seconds in the presence of 2-10, say 5 moles of hydrogen per mole of hydrocarbon. Product in line 46 includes 22.15 parts of an aromatic stream and 6.53 parts of light gases containing 6.90 parts of benzene, 7.95 parts of toluene, and 3.10 parts of xylene, 3.00 parts of C and 1.20 parts boiling above 345F. The components boiling up to 345F are flashed off in tower 48; and 1.20 parts of heavy material containing 1.0 parts of dicyclic aromatics are drawn off through line 49. The flashed-off components are passed through line 50 to line 35. Although not normally required, the flow sheet provides for draw-off or make-up of various streams through lines 23, 36, 39, 47, and 45. The overhead stream is passed through line 50 and combined with the stream from line 34 into lines 35 and 15 from which it is passed to tower 17. The so-recycled stream in line 15 contains 15.28 parts of benzene, 21.36 parts of toluene, and 15.55 parts of C aromatics.

The fused ring polycyclic aromatic hydrocarbons which are prevented from contacting the transalkylation catalyst in practice of the process of this invention are particularly undesirable in that inter alia they may lay down on this catalyst a resinous or polymeric deposit (including that formed by reactions of the double bonds in many of these materials); and this deposit is peculiarly able to decrease the activity of the catalyst.

It appears that the compounds which are to be removed in practice of this invention are not primarily characterized by boiling point. For example indane (b.p. 352F), naphthalene (b.p. 424F), indene (b.p. 360F) etc. all possess boiling points lower than eg pentamethyl benzene (b.p. 446F), etc.: the latter compound is a suitable reactant in the conversion of benzene to C -C it is also a feature of the process of this invention that it permits more controlled operation. In prior practice as the transalkylating catalyst becomes spent, it has been common to increase the temperature of operation in an attempt to maintain the desired yield. Although this may raise the conversion to (or more accurately maintain it at) desired predetermined levels, this may change the selectivity or yield of desired product aside from the economically undesirable aspects of the higher temperature level. Use of the novel process of this invention permits one to operate for longer periods of time at one temperature (with attainment of substantially constant yield) or alternatively to increase the temperature by a lesser degree as the catalyst activity decreases.

in prior practice, the effect of catalyst deactivation has also been counteracted by increasing the partial pressure of hydrogen, this being commonly effected by increasing the hydrogen to hydrocarbon mole ratio or by increasing the vapor pressure. While this may retard catalyst deactivation, it undesirably increases hydrocracking with the generation of additional. light gases during transalkylation. The result is increased hydrogen consumption and loss of appreciable yields of desired liquid aromatic products.

Another advantage which might accrue by practice of the process of this invention is that the transalkylation catalyst may have a longer life prior to the point at which it must be discarded. Catalyst life may be a function of the number of regenerations; and a catalyst which must be frequently regenerated typically every few days, will not last as long as a catalyst regenerated every few months.

It is a particular feature of the process of this invention that it may be characterized by ready attainment of extended catalyst life and by maximum flexibility. In the preferred embodiment for example, it is possible to control the split in line 18 so that desired portions of material are passed through line 25. In certain instances for example, it may be desirable to pass all the material in line 18 through line 25. In this instance, the

..heavy component may be passed to transalkylation through lines 27, 27', 31, and 32 in which instance none of the fused polycyclics in stream 18 will be admitted to transalkylation.

charged to dealkylation may be passed through lines 27, 28, 44, and 41. In this latter instance, the flow in Similarly, the heavies lines 29, 43', 37, 38, and 40 may be zero.

' In an alternative embodiment, a portion e.g. 5-100%,

' typically less than all, say 50%, of the material in line 18 may be passed through line 25. In this instance, operation may be controlled to yield in line 27 an amount of heavies, so that when combined with the heavies in lines 29 and 30, heavies in line 31 are equivalent to the lights in lines 27 and 24. In this instance, the

flow in lines 28 and 44 may thus be zero. Other modes of attaining the desired control of charge to transalky- BEST AVAILABLE COPY component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component which comprises a. fractionating said charge monocyclic aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component;

b. separating fused polycyclic hydrocarbon component from at least a portion of said fractionated stream containing said heavier component and said polycyclic hydrocarbon component thereby forming (i) an enriched stream of said heavier compo nent containing a greater amount of said fused polycylic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycylic component and (ii) a denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component;

c. combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) less than all of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalbdation charge stream containing (i) lighter component, (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon the content of heavier component in said transalkylation charge stream;

(1. transalkylating, at transalkylating conditions in the presence of heterogenous transalkylating catalyst, said transalkylation charge stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, and (iii) a lighter component containing a smaller number of carbon atoms than does said middle component; and

e. withdrawing said transalkylate product stream.

2. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein in said charge aromatic monocyclic stream, said lighter component is bezezene, said middle component is toluene, and said heavier component is xylene.

3. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said separating operation includes distilling at least a portion of said fractionated stream containing said heavier component and said polycyclic component;

recovering as bottoms from said distilling operation said enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component; and

v dealkylated.

17 recovering as overhead from said distilling operation said denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component.

4. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 5-1 of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to said separation operation.

5. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said denuded stream containing said heavier component and said fused polycyclic hydrocarbon component, contains less than about 0.3% of said fused polycyclic hydrocarbon component based on said heavier component.

6. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said transalkylation charge stream contains O-0.2% of said fused polycyclic hydrocarbons based. on the weight of said heavier component.

7. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 095% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation.

8. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 40-60% of said fractionated stream containing said'heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation together with at least a portion of said separated enriched stream containing said heavier component and said fused polycyclic hydrocarbon component 9. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 095% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation together with substantially all of said separated enriched stream containing said heavier component and said fused polycyclic hydrocarbon component are 10. A method of treating a chaii ge monocyclic aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component which comprises a. fractionating said charge aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component;

b. separating fused polycyclic hydrocarbon component from at least a portion of said fractionated stream containing said heavier component and said polycyclic hydrocarbon component thereby forming (i) an enriched stream of said heavier component containing a greater amount of said fused dEST AVAILABLE COPY polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component and (ii) a denuded stream of said heavier component con- 5 taining a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component; combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) a portion of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalkylation charge stream containing (i) lighter component, (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon the content of heavier component in said transalkylation charge stream;

d. transalkylating, at transalkylating conditions in the presence of heterogeneous transalkylating catalyst, said transalkylation charge stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component;

e. withdrawing said transalkylate product stream;

1". passing said withdrawn transalkylate product stream to separating operation;

g. dealkylating at least a portion of the fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a product dealkylate stream; and

passing said product dealkylate stream to said fractionating operation.

11. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim wherein the portion the said fractionated stream passedt 0'. rationisthat rtionin e e l to orrn said transalkylation charge W T2. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 10 wherein at least a portion of said separated enriched stream of said heavier component, containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component, is passed to said dealkylating operation.

13. A method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component which comprises i a. fractionan'ng said charge monocyclic aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component;

b. separating fused polycyclic hydrocarbon compo nent from at least a portion of said fractionated combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) less than all of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalkylation charge stream containing (i) lighter component,

BEST AVAILABLE COPY (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon the content of heavier component in said transalkylation charge stream;

d. transalkylating, at transalkylan'ng conditions in the presence of heterogeneous transalkylating catalyst, including a Group VIII metal on an acid support, said transalkylation charge stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, and (iii) a lighter component containing a smaller number of carbon atoms than does said middle component; and

e. withdrawing said transalkylate product stream.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. :3 927 ,136

DATED :December 16, 1975 Q INVENTOR(S) :Robert M. Suggitt and John D. Odle It 15 certified that rror appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

claim 10, line 1 "change" should be -charge Signed and Scaled this Twenty-fifth Day of April I978 |SF.-\l.| Anon:

RU'IH NIASON LUTRELLF. F. PARKER l-im'xring ()jficer Acting ('ummixxium'r of Putenfx and Trademarks 

1. A METHOD OF TREATING A CHARGE MONOCYCLIC AROMATIC HYDROCARBON STREAM CONTAINING (I) A MIDDLE COMPONENT, (II) A HEAVIER COMPONENT CONTAINING MORE CARBON ATOMS THAN DOES SAID MIDDLE COMPONENT, (III) A LIGHTER COMPONENT CONTAINING A SMALLER NUMBER OF CARBON ATOMS THAN DOES SAID MIDDLE COMPONENT, AND (IV) A FUSED POLYCYCLIC HYDROCARBON COMPOMENT CONTAINING AT LEAST AS MANY CARBON ATOMS AS DOES SAID HEAVIER COMPONENT WHICH COMPRISES A. FRACTIONATING SAID CHARGE MONOCYCLIC AROMATIC HYDROCARBON STREAM TO FORM AT LEAST (I) A STREAM CONTAINING SAID LIGHTER COMPONENT (II) A STREAM CONTAINING SAID MIDDLE COMPONENT, AND (III) A STREAM CONTAINING SAID HEAVIER COMPONENT AND SAID FUSED POLYCYCLIC HYDROCARBON COMPONENT; B. SEPARATING FUSED POLYCYCLIC HYDROCARBON COMPONENT FROM AT LEAST A PORTION OF SAID FRACTIONATED STREAM CONTAINING SAID HEAVIER COMPONENT AND SAID POLYCYCLIC HYDROCARBON COMPONENT THEREBY FORMING (I) AN ENRICHED STREAM OF SAID HEAVIER COMPONENT CONTAINING A GREATER AMOUNT OF SAID FUSED POLYCYLIC HYDROCARBON COMPONENT THAN SAID FRACTIONATED STREAM CONTAINING SAID HEAVIER COMPONENT AND SAID FUSED POLYCYLIC COMPONENT AND (II) A DENUDED STREAM OF SAID HEAVIER COMPONENT CONTAINING A LESSER AMOUNT OF SAID FUSED POLYCYCLIC HYDROCARBON COMPONENT THAN SAID FRACTIONATED STREAM CONTAINING SAID HEAVIER COMPONENT AND SAID FUSED POLYCYCLIC COMPONENT; C. COMBINING (I) SAID FRACTIONATED STREAM CONTAINING SAID LIGHTER COMPONENT, (II) AT LEAST A PORTION OF SAID DENUDED STREAM, AND (III) LESS THAN ALL OF SAID FRACTIONATED STREAM CONTAINING SAID HEAVIER COMPONENT AND SAID FUSED POLYCCLIC HYDROCARBON COMPONENT THEREBY FORMING A TRANSALKYLATION CHARGE STREAM CONTAINING (I) LIGHTER COMPONENT, 8II) HEAVIER COMPONENT IN AMOUNT SUBSTANTIALLY EQUIVALENT TO SAID LIGHTER COMPONENT, AND (III) FUSED POLYCYCLIC HYDROCARBONS IN AMOUNT OF LESS THAN ABOUT 0.3% BY WEIGHT BASED UPON THE CONTENT OF HEAVIER COMPONENT IN SAID TRANSALKYLATION CHARGE STREAM; D. TRANSALKYLATING, AT TRANSALKYLATING CONDITIONS IN THE PRESENCE OF HETEROGENOUS TRANSALKYLATING CATALYST, SAID TRANSALKYLATION CHARGE STREAM THEREBY FORMING A TRANSALKYLATE PRODUCT STREAM CONTAINING (I) A MIDDLE COMPONENT, (II) A HEAVIER COMPONENT CONTAINING MORE CARBON ATOMS THAN DOES SAID MIDDLE COMPONENT, AND (III) A LIGHTER COMPONENT CONTAINING A SMALLER NUMBER OF CARBON ATOMS THAN DOES SAID MIDDLE COMPONENT; AND E. WITHDRAWING SAID TRANSALKYLATE PRODUCT STREAM.
 2. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein in said charge aromatic monocyclic stream, said lighter component is benzene, said middle component is toluene, and said heavier component is xylene.
 3. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said separating operation includes distilling at least a portion of said fractionated stream containing said heavier component and said polycyclic component; recovering as bottoms from said distilling operation said enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component; and recovering as overhead from said distilling operation said denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component.
 4. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 5-100% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to said separation operation.
 5. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said denuded stream containing said heavier component and said fused polycyclic hydrocarbon component, contains less than about 0.3% of said fused polycyclic hydrocarbon component based on said heavier component.
 6. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein said transalkylation charge stream contains 0-0.2% of said fused polycyclic hydrocarbons based on the weIght of said heavier component.
 7. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 0-95% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation.
 8. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 40-60% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation together with at least a portion of said separated enriched stream containing said heavier component and said fused polycyclic hydrocarbon component.
 9. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 1 wherein 0-95% of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component is passed to a dealkylating operation together with substantially all of said separated enriched stream containing said heavier component and said fused polycyclic hydrocarbon component are dealkylated.
 10. A method of treating a change monocyclic aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component which comprises a. fractionating said charge aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component; b. separating fused polycyclic hydrocarbon component from at least a portion of said fractionated stream containing said heavier component and said polycyclic hydrocarbon component thereby forming (i) an enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component and (ii) a denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component; c. combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) a portion of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalkylation charge stream containing (i) lighter component, (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon the content of heavier component in said transalkylation charge stream; d. transalkylating, at transalkylating conditions in the presence of heterogeneous transalkylating catalyst, said transalkylation charge stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component; e. withdrawing said transalkylate product stream; f. passing said withdrawn transalkylate product stream to said separating operation; g. dealkylating at least a portion of the fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a product dealkylate stream; and passing said product dealkylate stream to said fractionating operation.
 11. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 10 wherein the portion the said fractionated stream passed to the dealkylating operation is that porTion in excess of the substantially equivalent portion which is combined to form said transalkylation charge stream.
 12. A method of treating a charge monocyclic aromatic hydrocarbon stream as claimed in claim 10 wherein at least a portion of said separated enriched stream of said heavier component, containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component, is passed to said dealkylating operation.
 13. A method of treating a charge monocyclic aromatic hydrocarbon stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, (iii) a lighter component containing a smaller number of carbon atoms than does said middle component, and (iv) a fused polycyclic hydrocarbon component containing at least as many carbon atoms as does said heavier component which comprises a. fractionating said charge monocyclic aromatic hydrocarbon stream to form at least (i) a stream containing said lighter component, (ii) a stream containing said middle component, and (iii) a stream containing said heavier component and said fused polycyclic hydrocarbon component; b. separating fused polycyclic hydrocarbon component from at least a portion of said fractionated stream containing said heavier component and said polycyclic hydrocarbon component thereby forming (i) an enriched stream of said heavier component containing a greater amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component and (ii) a denuded stream of said heavier component containing a lesser amount of said fused polycyclic hydrocarbon component than said fractionated stream containing said heavier component and said fused polycyclic component; c. combining (i) said fractionated stream containing said lighter component, (ii) at least a portion of said denuded stream, and (iii) less than all of said fractionated stream containing said heavier component and said fused polycyclic hydrocarbon component thereby forming a transalkylation charge stream containing (i) lighter component, (ii) heavier component in amount substantially equivalent to said lighter component, and (iii) fused polycyclic hydrocarbons in amount of less than about 0.3% by weight based upon the content of heavier component in said transalkylation charge stream; d. transalkylating, at transalkylating conditions in the presence of heterogeneous transalkylating catalyst, including a Group VIII metal on an acid support, said transalkylation charge stream thereby forming a transalkylate product stream containing (i) a middle component, (ii) a heavier component containing more carbon atoms than does said middle component, and (iii) a lighter component containing a smaller number of carbon atoms than does said middle component; and e. withdrawing said transalkylate product stream. 